1. Field of the Invention
The present invention relates to an optical lens, an LED module having the optical lens, and a lighting apparatus, such as a streetlight, having the LED module.
2. Description of the Related Art
Recently, the development of a lighting technique advantageous in terms of environmental friendliness and energy efficiency has emerged as an important issue. Coupled with this, a light emitting diode (LED), having a high efficiency and a long lifespan, as compared with other competing light sources, has been proposed as an alternative to substitute for existing light sources such as an incandescent electric lamp, a fluorescent lamp, and the like. The LED requires a suitable optical system to generate a proper light distribution according to an application field.
General streetlight illumination has light distribution characteristics in which light is spread widely in a direction of a lane axis of a roadway, rather than a symmetrical light distribution, when compared with general indoor illumination or other general illumination. The general street illumination is required to satisfy a light distribution standard according to the width of a road on which streetlights are installed, an amount of vehicle movement thereon, a vehicle speed limit, and the like, and the intensity of illumination and the standard of uniformity ratio of luminance according to the light distribution standard. A general lamp (e.g., a metal halide lamp, an incandescent electric lamp, a fluorescent lamp, and the like) has 360-degree light distribution, so streetlights using such a general lamp implement a side extended light distribution scheme by using a reflector on a rear surface thereof.
However, a streetlight using an LED as a light source cannot adjust a light distribution by using the reflector used for a general streetlight because light is emitted forwardly from an output surface of the LED. Thus, the streetlight having an LED as a light source adjusts its light distribution by using an optical system such as a lens, or the like. A general lighting apparatus using an LED light source largely uses a rotation symmetrical lens. Such a type of lens is not favorably applied to a streetlight that requires a particular light distribution and may be used for illumination that requires a focused or uniform light distribution. An LED illumination lens used for a streetlight requires asymmetrical light distribution characteristics, so an aspheric lens having an asymmetrical shape is used. However, the existing aspheric, asymmetrical lens has a problem in that it is difficult to fabricate a mold for manufacturing a lens and fabrication costs are also increased.